Structure and fatigue-behaviour of an endurable, highly loaded natural interzone: the cemento-dentine junction

哺乳动物的牙齿通过牙周膜和牙骨质悬置在颌骨内，牙骨质几乎覆盖了整个牙根。牙本质和牙骨质是两种硬度相似的矿化骨组织，它们通过一个薄的、更具顺应性的中间区-牙骨质-牙本质连接部（CDJ）连接。在人的一生中，数百万个咀嚼周期从牙本质经由CDJ转移到牙周组织。有趣的是，CDJ承受了数百万次的循环应力，没有临床报告的失败案例，即使它没有细胞重建和修复的能力。也许这种临床上的不明显性是为什么CDJ只有很少的研究，到目前为止，在InterDent研究小组的范围内，我们的目标是在项目2中更好地了解微观结构和疲劳性能之间的关系，这个持久的牙本质和牙骨质之间的中间地带。我们希望阐明导致其持久抗疲劳性的设计原理。此外，我们希望了解区域性不同的载荷条件是否反映在CDJ的微结构和纳米结构局部变化中，以及时间载荷变化是否导致CDJ结构和特性的适应性变化。为了实现这一点，我们计划i）研究CDJ的微结构和纳米结构以及微结构和纳米机械性能，以及物种，牙齿类型，性别和沿牙根表面的沿着位置; ii）分析源自牙齿病理或牙齿的年龄相关变化的对不同载荷条件的潜在形态-机械适应; iii）研究CDJ的微-和纳米-疲劳特性与沿着牙根表面局部变化的体内载荷条件的关系。我们将更好地理解CDJ的结构/性能关系和功能，这将使我们能够推导出构成两种较硬材料之间的耐用和抗疲劳中间区的一般材料科学原理。最终，通过这种方式，CDJ将成为牙科及其他领域生物灵感设计的榜样。

Mammal teeth are suspended within the jaw via the periodontal ligament and the dental cementum which covers dentine nearly all over the root. Dentine and cementum, two mineralised bony tissues of similar stiffness are connected by a thin, more compliant interzone, the cemento-dentine junction (CDJ). Over the human lifespan, millions of chewing cycles are transferred from dentine via the CDJ to the periodontal apparatus. Interestingly, the CDJ endures these millions of cyclic stresses, with no clinically reported cases of failure, even though it has no capacity of cellular re-modelling and thus repair. Maybe this clinical inconspicuousness is the reason why the CDJ has only sparsely been investigated, so far.Within the scope of the research group InterDent, we aim in project 2 at better understanding the relationship between microstructure and fatigue properties of this endurable interzone between dentine and cementum. We want to elucidate the design-principles leading to its long-lasting fatigue resistance. Further, we wish to understand whether the regionally different loading conditions are reflected in micro- and nano-structural local variations of the CDJ and whether temporal load changes lead to adaptive changes in the CDJ structure and characteristics.To achieve this, we plan i) to characterise the micro- and nanostructure as well as the micro- and nano-mechanical properties of the CDJ, and the influence of species, tooth type, sex and location along the root surface; ii) to analyse potential morpho-mechanical adaptations to different loading conditions, originating from tooth pathologies or age-related changes of the tooth; iii) to investigate the micro- and nano-fatigue properties of the CDJ in relation to locally varying in vivo loading conditions along the root surface.Thus, we will gain a better understanding of the structure/property-relationship and the function of the CDJ, which will allow us to derive general material science principles that constitute a durable and fatigue-resistant interzone between two stiffer materials. Ultimately, this way, the CDJ will serve as a role-model for bio-inspired design of such interzones, in dentistry and beyond.